The present inventive subject matter relates to the document printing arts. It is particularly applicable to marking engines, such as printers, copiers, facsimile machines, multifunction machines, xerographic devices, etc., and it will be described with particular reference thereto. However, application is also found in connection with other marking engines and/or implementations.
Some marking engines apply toner on a page or sheet of paper or other suitable image receiving medium (e.g., transparencies, etc.) to form an image thereon. Commonly, after the toner is applied, a process known as hot roll fusing uses heat and pressure to bond or fuse the toner to the page thereby fixing the image thereon.
For example, FIG. 1 shows a typical hot roll fusing station or assembly 10. The station 10 includes a fuser roller 12 and a pressure roller 14 that rotate in the directions of arrows 15 and 16, respectively. The fuser roller 12 commonly takes the form of a hollow tube 17 containing a heating element, usually a quartz rod or lamp 18, which heats up when electrical power is supplied thereto. Generally, the fuser roller 12 has a hard metal tube 17 that may be coated with Teflon® or a soft vinyl, and the heat from heating element is conducted from the rod or lamp 18 to the surface of the roller tube 17.
In hot roll fusing, the page 20 with dry toner particles thereon moves between the two rollers 12 and 14. The pressure roller 14, usually having a silicone rubber outer layer, presses the page 20 against the fuser roller 12. When the page 20 passes between the rolls, the heat of the fuser roller 12 and pressure applied by the pressure roller 14 melts the toner and fuses it to the page 20. The pressure roller 14 ensures that the page 20 is pressed against—and a little around—the fuser roller 12. This helps force the melted toner into the page. If the pressure roller 14 were a hard roller, the page 20 would be against the heated fuser roller 12 at only one point on the roll. On the other hand, a softer pressure roller 14 conforms the page 20 to the curved shape of the fuser roller 12 and ensures long enough contact therewith to completely melt the toner. This contact region is referred to as the nip and can be described by an amount of pressure thereat and/or the area of contact, e.g., a width in the direction of page movement and a length in the axial direction or direction normal to that of page movement.
It is generally advantageous to carefully control the temperature of the fuser roller 12 so that enough heat is supplied to melt the toner into the page 20 but not so much that it could damage the image. However, axial temperature uniformity tends to be difficult to achieve with traditional fuser rollers 12. Relatively cooler spots along the axial length of the fuser roller 12 can result in ineffective melting of the toner at that axial position, and relatively hotter spots along the axial length of the fuser roller 12 can result in image damage at that axial location. Accordingly, in an effort to address this issue, some marking engines employ two or more fusing stations 10 or quartz lamps 18 of different axial lengths to handle pages of different widths. Such implementations however can be disadvantageous as the separate independent fusing stations 10 or quartz lamps 18 present added production cost and/or other drawbacks that normally attend the use of additional components.
It is also generally advantageous that the fuser roller 12 be sufficiently stiff so as not to deform under the pressure of the pressure roller 14. Such deformation can result in distortions to the image. In an effort to address this issue, traditionally the tube 17 of the fuser roller 12 has been constructed with a suitably thick wall and/or reinforcements therefor. However, this solution tends to increase the thermal mass of the fuser roller 12 thereby disadvantageously increasing the warm-up time as compared to an otherwise similar fuser roller 12 with a relatively thinner tube wall and/or less or no reinforcements. That is to say, the thicker the wall is and/or the more reinforcements that are used, then the higher the thermal mass the fuser roller 12 will have, and hence, a greater warm-up time.
The present inventive subject matter contemplates a new and improved hot roll fusing station and/or hot roll fusing method that overcomes the above-mentioned limitations and others.